Defense in Depth is a fundamental security strategy that relies on multiple layers of defense to protect information and systems. The concept is borrowed from military strategy: if one line of defense is breached, others are in place to stop or slow down the attack.
The Layered Approach
A robust Defense in Depth strategy includes controls at various levels:
🏢 Physical Layer
Fences, locks, guards, and cameras protecting data centers.
🌐 Network Layer
Firewalls, intrusion detection/prevention systems (IDS/IPS), and network segmentation.
💻 Host Layer
Antivirus, endpoint detection and response (EDR), and patch management on individual devices.
📱 Application Layer
Secure coding practices, web application firewalls (WAF), and rigorous input validation.
💾 Data Layer
Encryption (at rest and in transit) and access controls.
Why It Matters
No single security control is perfect. Software has bugs, users make mistakes, and hardware fails. By layering defenses, we ensure that a failure in one component does not result in a catastrophic breach. This approach increases the cost and difficulty for an attacker, often deterring them or providing defenders enough time to detect and respond to the intrusion.